I got absolut the same problem here with two Servs but running with apache2 webserver.
After upgrade of
apport:amd64 (2.20.9-0ubuntu7.18, 2.20.9-0ubuntu7.19), python3-apport:amd64 (2.20.9-0ubuntu7.18, 2.20.9-0ubuntu7.19), erlang-eimap:amd64 (0.4.2-2.1, 0.4.3-1.1), guam:amd64 (0.9.7-3, 0.9.8-1), guam-libs:amd64 (0.9.7-3, 0.9.8-1), python3-problem-report:amd64 (2.20.9-0ubuntu7.18, 2.20.9-0ubuntu7.19)
roundcube doesn't work...